This invention relates to roller conveyors, and more particularly to improvements in the drive systems of such conveyors.
Many different systems have been employed for driving the conveyor rollers. For example, metal chains on sprocket wheels have been used to drive the rollers, but the chains tend to be very noisy and require significant power to drive. The metal chains also cause significant vibration in the conveyor, which is especially undesirable in conveyors moving sensitive or fragile articles such as electronic components. Plastic chains, such as ladder chains, are generally quieter and less vibrational than metal chains but often lack sufficient strength to reliably drive large groups or a long series of sprocket wheels. The problem is that these ladder chains tend to break or split at or near their splicing locations as well as at their transverse crosspieces or rungs.
Frictional drive belts such as V-belts and O-rings have been used as an alternative to chains. These frictional belts generally rely solely upon friction between the belt and pulleys (connected to the conveyor rollers) to transmit power. However, frictional belts have been known to be limited in the number of pulleys that can be effectively driven by one belt without a significant drop in the rotation speed of the conveyor rollers farthest from the power source. To avoid large variations in the speed of movement of an article on the conveyor, more power sources must be used. In an attempt to promote better power transfer to the driven pulleys, idler pulleys have often been added to the drive system to increase the tension on the belt and also to serpentine the belt around the driven pulleys to cause more drive contact therebetween. However, these idler pulleys have been of only limited effectiveness in enhancing the power transfer while dissipating power and reducing the efficiency of the conveyor's drive system.
Positive drive belts and flanged driven pulleys combined with idler pulleys for serpentining the drive belt are proposed for conveyors in Blocker U.S. Pat. No. 5,040,669, but the idler pulleys and serpentine belt arrangement increase the complexity, weight and potential vibration of the conveyor, as well as the power consumption.